1. —Field of the Invention
The embodiments described herein relate to the field of laser-based surgical procedures for ophthalmology. More particularly, the embodiments relate to the field of laser-based surgical procedures for the treatment of glaucoma.
2. —Description of Related Art
Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. An increase in intraocular pressure (IOP) is often associated with glaucoma. IOP is a function of episcleral venous pressure, the production of aqueous humor within the anterior chamber of the eye, and its outflow through the trabecular meshwork and the uveoscleral pathway. The aqueous humor is a clear liquid that primarily fills the Anterior Chamber (AC, FIG. 1, 30). The aqueous humor is produced by specialized cells in the Ciliary Body (FIG. 1, 70). Aqueous humor drains through the Trabecular Meshwork (TM. FIG. 1, 100), whose Juxtacanicular Trabecular Meshwork (JCT, FIG. 1, 110) lines Schlemm's Canal (SC, cf. FIG. 1, 150) allowing flow into the away from the AC. Schlemm's Canal (SC, cf. FIG. 1, 150) is coupled to a network of collector channels allowing the aqueous humor to be absorbed by the body as it is drained away from the eye.
There are mainly two surgical strategies to manage glaucoma and the pathologies associated with it that involve minor invasive surgery. One strategy is by affecting the generation of aqueous humor (e.g. reducing it) in the eye. The other strategy is augmenting drainage of the fluid out of the eye's cavities, through Schlemm's Canal. According to the first strategy, a method called endoscopic cyclophotocoagulation (ECP) uses a laser beam to stunt the Ciliary Body. The production of aqueous humor by the stunted cells is then reduced significantly, resulting in a lowering of IOP. ECP is a bi-manual procedure that requires endoscopic visualization to precisely target and gauge the laser action on the Ciliary Body in real time.
According to a second strategy, the TM outflow path may be bypassed. There are different ways to achieve this. Some of these techniques utilize laser ablation of the TM to gain direct access to SC and the collector channels. For example, Selective Laser Trabeculoplasty (SLT) utilizes a laser to target intracellular melanin. To perform SLT, a frequency doubled (532 nm) Q-switched Nd:YAG laser with a 400 μm spot size may be used. The laser may be operated in pulsed mode to deliver 0.4-1 mJ of energy for about 0.3 ns (nanoseconds). This may produce a biological effect on the TM, stimulating a mechanism to enhance aqueous outflow from the eye via SC. SLT protects the TM against thermal or coagulation effects by selectively targeting the pigmented cells in the eye. Thus, surrounding tissue may be preserved. However, in eyes with little pigmentation the laser may target only a limited area. Another technique of choice may be Argon Laser Trabeculoplasty (ALT). ALT consists in the opening of the drainage angle of the eye by simply piercing through the TM via tissue ablation. However, this technique may induce thermal damage to the surrounding tissue, scarring it. Once scar tissue develops surrounding the area of interest it becomes difficult to repeat the procedure in the same area, or its vicinity. Also, scar tissue may block the drainage of aqueous humor into SC.
Further within the second strategy, some approaches may include the use of a stent, or “shunt” surgically implanted in the eye via an ab-interno procedure. In some cases the implant may provide a tube or conduit that pierces through the TM, allowing aqueous humor to flow out of the eye via the SC and collector channels. However, these devices may easily bend or occlude as the area heals rendering the bypass less effective over time.
Therefore, there is a need for a minimally invasive Trabeculectomy procedure that limits tissue ablation to the Trabecular Meshwork only, causing minimal damage in the surrounding tissue.